Rapid Spread of Onion Downy Mildew, Urgent Need for Prompt Control Measures

Published 09 Mar.2021 10:35(KST)

Updated 12 Aug.2025 13:46(KST)

High Temperatures and Heavy Rainfall Since Late February in Gyeongnam This Year Lead to Increased Spread of Leaf Spot Disease

Onions affected by downy mildew.

[Asia Economy Yeongnam Reporting Headquarters Reporter Park Saeyan] The Gyeongsangnam-do Agricultural Research and Extension Services announced that downy mildew is rapidly occurring and spreading in major onion production areas within the province, urging timely control measures.

The optimal temperature for the outbreak of onion downy mildew is 10?12℃, and if moisture remains on the leaf surface for more than 2 hours, it becomes easier for pathogens to invade, increasing the infection rate.

Since late February this year, the highest temperature in Gyeongnam has been 13.2℃, which is 2.5℃ higher than the average year.

Relative humidity is 10.3% higher, and precipitation is also abundant at 20.2mm, causing downy mildew to rapidly occur in the province.

Onion downy mildew occurs in primary and secondary phases. The primary outbreak occurs from mid-February to mid-March when temperature and humidity rise, allowing the fungus to invade onion leaves.

The cause of occurrence is infection during seedling cultivation or pathogens present in the soil during winter.

The secondary outbreak occurs after April, when the pathogens from the primary infection form conidia and spread to neighboring plants through the wind.

Therefore, controlling the primary inoculum that occurs in early spring as early as possible can reduce secondary infections.

Onion plants damaged by the primary downy mildew infection do not respond well to control measures, so suspected plants should be uprooted and burned during the early symptom stage, and appropriate pesticides should be applied.

Applicable pesticides include systemic fungicides (Dimethomorph, Metalaxyl, etc.) and protectants (Mancozeb, Chlorothalonil, etc.), and it is advisable to spray the appropriate amount 4?5 times at intervals of 7?10 days.

Moon Jinseong, an agricultural researcher at the Yangpyeong Onion Research Institute, emphasized, "Since this month marks the beginning of primary downy mildew activity, uprooting and burning infected plants during this period and applying pesticides can reduce secondary outbreaks."